Hiro says that his apartment was bought for him by his parents as a bonus for "managing to get through four years of college". (Chapter 7)

Hiro's Tokyo apartment had a filthy bathtub, food-specked dishes, and rumpled piles of clothes. Because Hiro never bothered to pay attention tot he state of his home, he feels this is a surefire way to repulse women. (Chapter 12)

Hiro tells Charlie that he has a book of the Kensei Tapestries at home. (Chapter 13)

Trivia

Hiro has a poster of Ninja Skrull. This probably references Ninja Scroll, a violent Japanese action thriller anime.

Hiro has a poster of a motorcycle that says "Akira". This probably references Akira, the animated film by Katsuhiro Otomo about a motorcycle gang in the future. Various explosions are critical plot points.

Hiro has a poster that says "Love Bina". This probably references Love Hina, the popular manga and anime series by Ken Akamatsu.

Hiro has a poster that says "Fathom". This probably references Fathom, a comic book created by Michael Turner for Aspen about a female superhero with water-based powers.

The rightmost poster seems to have the letters "G" on the top and "SHE" further down, likely referencing the popular cyberpunk manga and anime series Ghost in the Shell. The face on the poster also seems to be wearing a visor or glasses like Motoko on the cover art of the first movie.